The use of flexible couplings for interconnecting driving and driven shafts of precision instruments wherein the coupling is capable of accommodating shaft misalignments and axial shaft movements and permits limited torsional or radial deflection thereof is well known. In selected portions of an article entitled “Radial-Beam Couplings: A Cut Above the Rest” (Machine Design; Jul. 6, 2000) John B. Ricker states: “Of the many types available, single piece flexible couplings are the least expensive, and common geometries include radial slotted beam, helical or spiral, and bellows. The most critical factors to consider when choosing flexible couplings include torque capacity, torsional stiffness, bearing loads, transmission errors, shaft misalignment, and service life. Torque capacity is a measure of the coupler's amount of angular or parallel offset allowed from motor to load, and the life expectancy of the coupling. That is, stiff couplings operating under relatively high stress from large offsets can't survive millions of operating cycles. Transmission errors manifest themselves as small variations in velocity and position between motor and load. The variations are due primarily to coupling geometry and relative size. Bellows couplings usually provide the lowest transmission errors and radial bearing loads, good lateral flexibility, and the highest torsional stiffness. However, they have lower peak and running torque for equivalent sizes and are the most expensive. Bellows couplings have been traditionally used in smaller stepmotor and servomotor-driven systems. By comparison, helical or spiral couplings have sufficient lateral flexibility to handle large shaft offsets. But they also have only moderate torsional stiffness and the largest transmission errors. Helical couplings are generally categorized by the number of starting slots. For example, a single-beam helical coupling has one continuous cut throughout its entire one-piece flexing or working length. By contrast, a six-beam coupling has two sets of three helical cuts 120° apart separated by a center piece. A hub at each end of the coupling connects the motor drive shaft to the load, or feedback devices such as resolvers and encoders to lead screws and power transmission components. Ordinary radial beam slotted-type couplings fall between the above two types for cost, torsional stiffness, and transmission errors (driving an encoder), but produce the highest radial bearing load.”
An example of a helical flexible coupling is shown by U.S. Pat. No. 4,203,305 (Williams; 1980) which discloses a flexible coupling for torque transmission having a plurality of helical beams extending between the coupling ends.
An example of a radial beam slotted-type coupling is shown by U.S. Pat. No. 5,299,980 (Agius; 1994) which discloses a constant velocity flexible coupling for coupling two shafts that has a solid unitary body (22) with a plurality of complimentary pairs of slots (e.g., 34 paired with 36) positioned between a first and second end (hubs 24, 26). The plurality of complimentary pairs of slots extend inwardly from the circumference of the (cylindrical) body to a predetermined depth so as to form a plurality of beams (e.g., 46) between the complimentary pairs of slots. A plurality of disks (e.g., 111, 112) are formed in the body by the plurality of complementary pairs of slots, and the plurality of beams join and bridge the space between adjacent disks. Adjacent beams (e.g., 46, 64 or 78, 84) are angularly offset by a number of degrees (e.g., 90 degrees or e.g., 30 degrees). The illustrations (FIGS. 1–16) show that the “complimentary pairs of slots extending inwardly from the circumference of the body to a predetermined depth” form radial beams that are centered on diameters of the cylindrical beam, i.e., the “predetermined depth” is the same for each of the slots in a “complimentary pair of slots”.
As stated in the Ricker article hereinabove, radial beam slotted-type couplings fall between the bellows and helical types of flexible couplings in terms of cost, torsional stiffness, radial bearing load, and transmission errors. It is an object of the present invention to provide a novel flexible coupling that achieves performance advantages of both the bellows type and the slotted radial beam type while maintaining the low cost advantage of slot and beam types of flexible couplings.